Antenna



Sept. 29, 1959 c. w. ENDRES 2,907,035

ANTENNA Filed Dec. 10, 1956 6 /14/5256 it. E/VDRES' INVENTOR.

United I States Patent ANTENNA Charles W. Endres, Reseda, Calif., assignor to Bahcoclr Radio Engineering, Inc., Van Nuys, Calif., a corporation of California Application December 10, 1956, Serial No. 627,165 Claims. or. 343-814) This invention relates generally to improved antenna arrangements, and more particularly has to do with antenna assemblies wherein electromagnetic energy is fed to antenna elements through coaxial lines, the invention teaching the advantageous use of particular coaxial lines for both feeding and supporting the antenna elements in such a way as to minimize radiation losses from the feed line and to maximize desired radiation from the antenna elements themselves. The invention finds particular application to directional antenna assemblies as will be described, and when so used and applied it permits increased power gain in the preferred radiation direction or directions as compared with gains obtainable from conventionally fed, similar antenna arrays.

Among the basic considerations to be taken into ac: count in the design of antenna systems capable of efficiently radiating or receiving electromagnetic wave energy 7 2,907,035 Patented Sept. 29,1953

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factor while assuring maintenance of desirable insulating qualities of the feed line. Furthermore, the conductors are effectively shielded from the antenna elements to which they are connected by connecting lines extending from the tube interior to the various plural antenna elements to be driven. As a result, the elements can be desirably spaced along the boom and phased as respects maximum energy radiating efficiency and current flow along the elements since the wave velocities along the conductors in the boom in the direction of antenna element separation are substantially the same as the velocities of electromagnetic waves radiated in that direction in space by the driven elements. 7

These and other objects and advantages of the invention, together with the details of certain typical and pre ferred embodiments, will be more fully understood to best advantage from the following description of the accompanying drawings, in which:

Figure l is a perspective view of one embodiment of the invention;

Figure 2 is a section taken on line 2-2 of Figure 1; Figure 3 is a section taken on line 33 of Figure l; and

Figure 4 is a perspective showing of a modified form of the invention. The Figure 1 showing represents an application of the invention to a particular directional antenna, it being are the various phase relationships of electrical current flowing in the antenna elements, in relation to the arrangement of the elements in air and their relative spacing. These considerations are in turn related to the particular electrical characteristics of the means through which electromagnetic wave energy is transmitted to or from the elements and the method of supporting the antenna elements in air. For example, it is well known that the dielectric properties of the feed line or lines through which energy is led to antenna elements affects the phasing of current flowing in the elements, which in turn affects their combined radiating characteristics, and the element supports and separate feed lines in conventional antenna arrays contribute to lessened element radiating efliciency through radiation losses from the feed lines and the tendency of supports near the antenna elements to distort the electromagnetic radiation field.

Feed lines utilizing solid insulating materials such as plastic are characterized, insofar as wave energy transmission is concerned, as having associated wave velocity factors, which may be defined for a given line as the ratio of the velocity of wave transmission along the line to the radiated wave velocity in air or space. Such velocity factors, which for plastic insulated coaxial cable may be around 65%, must be taken into consideration 'in determining the current phase relationships as respects the antenna elements fed by transmission lines, and in the past antenna systems were necessarily made undesirably. complex as regards feed lines and antenna elements required for efficient operation.

The present invention is predicated on the concept that a simple and efiicient antenna system can be achieved, having many desirable operating characteristics, by combining the feed lines and antenna element supports into a single boom arrangement the velocity factor of which approaches unity. One and preferably two conductors extend within elongated hollow metallic means such as a tube supporting the antenna elements, and the space between the conductors and the tube is filled with a substance having a dielectric constant approximately the same as that of air, giving a high velocity understood however that the improvements discussed in connection with the drawing may be carried into many other forms of antenna arrays and assemblies in which two or more driven antenna elements are supported by a common feed line.

The three antenna elements 10, 11 and 12 in the fornij of elongated rods are shown extending in a plane and parallel to one another, and they may be conveniently further identified by the capital letters R, A and D corresponding to the designations reflector, antenna and director normally associated with parasitic antenna arrays. These elements are not parasitic in the sense that term is used in connection with antenna arrays, inasmuch as they are each electrically connected with a pair of conductors 13 and 14 to be excited in response to electromagnetic wave energy transmitted from circuit 15 to the antenna elements via the input leads 16 and 17 and conductors 13 and 14.

The parallel conductors extend Within a metal tubular boom 18 and are supported in spaced relation to the tube wall by a minimum number of axially spaced, wafer type insulating supports 19, as shown in Figure 3. Moreover, the space 20 between the conductors and the inner wall of the open-ended tubular support 18 is filled with air, so that the velocity factor of wave energy transmis sion along the conductors is as high as 97 to 99%, where: as the velocity factor associated with a coaxial line filled with plastic insulation might be as low as 65%. Other substances having dielectric constants approximately the same as that of 'air may also be used, a typical example being the commercial air bubble filled product known as Foamite.

The two conductors are symmetrically ofiset on opposite sides of the tube axis, and they typically lie in a plane parallel to the plane of the antenna elements, so that the three sets of T-match connections 21 and 22, 23 and 24, and 25 and 26 may extend from the conductors parallel to the antenna elements before turning at right angles and connecting with those elements. Whereas the intermediate connections 23 and 34 extend laterally through suitable insulators 27 in the wall of tube 18, the connectors 21 and 22, and 25 and 26 extend from the free ends of the conductors at the tube open ends to the elements 10 and 12.

The antenna elements shown have lengths approximate- .ergy to be radiated at the selected design frequency, and

they are conveniently centrally supported on the tubular boom 18 as by ring clamps 28 at the intervals X- and Y between elements 11 and 12, and elements and 11. With the boom electrically grounded as illustrated, the portian of each antenna element projecting from a clamp 28 becomes an efiective quarter wave length antenna fed near its grounded end, inasmuch as the T-match connections are much shorter than the lengths of the antenna elements themselves. The exact points on the antenna elements to which the T-connections are joined may be determined experimentally so that no power is reflected back to the transmitter associated with circuit 15.

The conductors 13 and 14 are normally driven a half wave length out of phase, lines 16 and 17 being attached to the conductors at any current node along their extent. In order to realize optimum gain in the transmission direction indicated by the arrow 30, the driven antenna elements may be spaced at intervals X and Y not necessarily equal and normally no greater than a quarter wave length, the spacing being determinable by experiment. Therefore, in order to obtain proper cancellation and reinforcement of radiated electromagnetic waves for radiation directing purposes, the lengths of elements 10 and 12 must be respectively slightly longer and slightly shorter than one-half wave length to be sufiiciently inductive and capacitive to produce the required time phasing as related to the inter-element intervals X and Y traversed by the radiated wave energy. A typical example would be as follows:

Frequency 14 megacycles. Length of element 10 35 feet 3 inches. Length of element 11 33 feet.

Length of element 12 31 feet 8 inches. Distance X .15 wave length. Distance Y .lll wave length.

Other advantages of the assembly include the fact that the diameters of the conductors 13 and 14 may be varied in relation to the diameter of tubular boom 18 to obtain any desired characteristic impedance. Also, the conductors 13 and 14 remain completely shielded at all times,

preventing radiation losses during feeding of the antenna elements, and the antenna system as a whole is balanced since the half wave antenna elements are grounded at their centers and the capacitance between-the conductors and the grounded tube 18 is uniform along thelengths of the conductors. Measured forward gain characteristics of this antenna assembly have been found superior to the parasitic type antenna with similar antenna elements.

The modified antenna assembly shown in Figure 4 is similar to that of Figures 1 through 3 with the exceptions that only one conductor 40 extends within the grounded tubular boom 18, and the antenna elements 41, 42 and 43 are only half as long as the corresponding elements 1' 11 and 12 previously described. The parallel, approximate quarter wave length elements 41, 42 and 43 extend laterally from their connection with the boom 18 at only one side thereof, and therefore gamma type connections 44, 45 and 46 are utilized for connecting the single conductor 40 to the antenna elements.

I claim:

1. An improved antenna assembly, comprising a 1ongitudinally elongated metallic tubular boom, a plurality of longitudinally spaced antenna elements supported by said boom in substantially parallel relation, each element including symmetrical right and left portions projecting laterally at opposite sides of the boom, said elements throughout their lengths extending outside the boom interior and being electrically connected with the boom at support locations, a pair of selectively separated elongated parallel conductors extending longitudinally within the boom and spaced from the inner side thereof, and connectors separately connecting the element right and left portions with said respective conductors so that each element portion projecting at a side of the boom is individually electrically connected with only one of said conductors, each of said connectors being connected with a conductor within the boom and with an element portion at a selected position exterior of the boom and spaced from the element support location, the spacing between each ele ment support location and the position at which the connectors are connected with the element right and left portions being substantially equal, and substance intermediate said conductors and the inner wall of the boom and having a dielectric constant approximately the same as that of air.

2. The invention as defined in claim 1 in which said connectors are connected to said elements at positions selected so as to match the impedances of said elements and conductors, and including feeder lines connected with said conductors for feeding input electromagnetic energy thereto, said conductors being selectively spaced apart laterally within the boom so as to match the impedances of said conductors and feeder lines.

3. The invention as defined in claim 1 in which three antenna rod elements are supported by said boom, and in which one of said conductors is electrically connected with the right portions of the intermediate and another element and the left portion of the remaining element, and in which the second conductor is electrically connected with the left portions of the intermediate and said other element and the right portion of said remaining ele- 'ment.

References Cited in the file of this patent UNITED STATES PATENTS 2,557,941 Casabona "June 26, 1951 2,641,702 Cohen June 9, 1953 FOREIGN PATENTS Germany May 16, 1942 

